The invention relates to a rubber composition with increased dispersion of the reinforcing filler in the rubber elastomer.
Rubber compounding refers to the process of adding various materials to the rubber polymer to achieve desirable physical and chemical properties. During compounding of a typical rubber composition, vulcanizing agents, accelerators, fillers, plasticizers and antidegradants are added to the polymer.
Dispersion of fillers and pigments involves the process of uniformly incorporating those materials into the rubber elastomer and includes reduction of their sizes. More complete dispersion results in a rubber compound having more consistent physical and chemical properties throughout the bulk of the compound, which yields a better finished product. With fillers in particular, dispersion involves the reduction of the original, large agglomerates, comprised of many individual aggregates. The original agglomerates are reduced to a combination of individual aggregates, and agglomerates much smaller than the original ones. The reduction in the size and number of agglomerates provides a better finished product.
Historically, mechanical mixing equipment, such as an open mill, an internal mixer, or a batch mixer/extruder combination, has been utilized to aid in the dispersion of fillers within the elastomer. Often the incorporation of filler into elastomer occurred by mechanical mixing which used multiple mixing stages, including masterbatching, remill, and final mixing. Alternatively, U.S. Pat. No. 5,599,868 discloses a method for mixing a rubber composition with improved properties, comprising the steps of treating a filler with liquid in the amount of 10-60% by weight to form a pre-blend, and mixing the pre-blend with at least one polymer.
The present invention solves problems in the art of reducing agglomerate sizes of a reinforcing filler in a rubber elastomer during the mixing process of rubber compounds, preferably for forming pneumatic tires.
The present invention is directed to a process for compounding polymer and filler with a polar surfactant which results in reduced overall mixing time when compared to existing compounding-mixing techniques.
More particularly, the present invention employs an organic, polar surfactant to break down the water soluble binder used in carbon black pelletization to aid in the dispersion of the carbon black into the elastomer. The properties of the organic, polar surfactant, such as its molecular weight and polarity, and the amount of surfactant in the compound, control the degree of dispersion of the reinforcing filler in the elastomer. The surfactant acts upon the water-soluble binder that otherwise hinders dispersion of the carbon black filler throughout the rubber elastomer.
One aspect of the present invention is a vulcanizable elastomer composition having approximately 100 parts by weight of a polymer, about 5 to about 100 parts by weight of a reinforcing filler per 100 parts polymer, about 0.5 to about 10 parts by weight of a polar surfactant per 100 parts polymer and about 0.5 to about 15 parts by weight of cure agents per 100 parts of said polymer.
Another aspect of the invention is a process for preparing an elastomeric composition with increased dispersion of filler in the composition, comprising the steps of (a) mixing reinforcing filler, polar surfactant and polymer to form a rubber compound; (b) curing the rubber compound to form the composition; wherein the polar surfactant has an hydrophilic-lipophilic balance value of about 3 to about 35.
Another aspect of the present invention is to provide a rubber product, comprising at least one rubber component having reinforcing filler and a polar surfactant, wherein the filler has increased dispersion in the rubber component due to the incorporation of the polar surfactant, and wherein the polar surfactant has an hydrophilic-lipophilic balance value of about 3 to about 35.
An advantage of the invention is the ability to provide fewer filler agglomerates and reduced agglomerate sizes in the rubber compound with faster processing times.
Another advantage of the invention is the utility of the invention with any rubber compound that employs carbon black as a filler, where the carbon black is delivered to the mixing chamber in a pelletized form using a water soluble binder.